This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We have initiated the renal transplants planned for this study. In order to develop a clinically translatable regimen our previous regimen (Nat. Med. 2009;15:746-9) was modified: CTLA-4-Ig was replaced with the higher affinity belatacept. Alefacept was increased from 0.3mg/kg to 1.0mg/kg based on in vitro and in vivo studies, and sirolimus was delivered via intramuscular injection to better approximate clinical levels. Specific pathogen free rhesus monkeys (n=5) underwent MHC mismatched renal allotransplantation. Alefacept (1mg/kg) was given on days -1, 3, 7, and weekly for 8 weeks. Belatacept (10mg/kg) was given on days -1, 3, 7 and weekly (5mg/kg) for 24 weeks. Sirolimus was given daily to maintain a trough of 6-10ng/mL for 16 weeks. The regimen successfully prevented rejection in all 5 animals. Only after both alefacept and sirolimus were weaned did any animal show evidence of rejection. Flow cytometry was used to quantify and characterize T cell subsets. Alefacept induced a transient depletion of memory T cells - most notably CD8+ TEM cells. The proportion of CD2hi T cells dramatically diminished during alefacept treatment and returned to baseline after withdrawal, suggesting that alefacept selectively targeted those cells with the highest CD2 expression. Though this regimen did not produce tolerance, these data support belatacept, alefacept, and sirolimus as a translatable, CNI and steroid-sparing regimen for human kidney transplantation. We now are investigating Modified Vaccinia Virus Ankara strain vaccination as a means of inducing a tractable viral-specific T cell response to assess the effect of this regimen of protective immunity.